Xylan, a major component of plant hemicellulose, is a polymer of D-xylose linked by beta-1,4-xylosidic bonds. Xylan can be degraded to xylose and xylo-oligomers by acid or enzymatic hydrolysis. Enzymatic hydrolysis of xylan produces free sugars without the by-products formed with acid (e.g. furans).
Enzymes which are capable of degrading xylan and other plant cell wall polysaccharides are important for the food industry, primarily for baking and in fruit and vegetable processing such as fruit juice production or wine making, where their ability to catalyse the degradation of the backbone or side chains of the plant cell wall polysaccharide is utilised (Visser et al., Xylans and Xylanases, 1991).
Other applications for xylanases are enzymatic breakdown of agricultural wastes for production of alcohol fuels, enzymatic treatment of animal feeds for hydrolysis of pentosans, manufacturing of dissolving pulps yielding cellulose, and bio-bleaching of wood pulp [Detroym R. W. In: Organic Chemicals from Biomass, (CRC Press, Boca Raton, Fla, 1981) 19-41.; Paice, M. G., and L. Jurasek., J. Wood Chem. Technol. 4: 187-198.; Pommier, J. C., J. L. Fuentes, G. Goma., Tappi Journal (1989): 187-191.; Senior, D. J., et al., Biotechnol. Letters 10 (1988):907-912]. WO 92/17573 discloses a substantially pure xylanase derived from the fungal species H. insolens and recombinant DNA encoding said xylanase. The xylanase is stated to be useful as a baking agent, a feed additive, and in the preparation of paper and pulp.
WO 92/01793 discloses a xylanase derived from the fungal species Aspergillus tubigensis. It is mentioned, but not shown that related xylanases may be derived from other filamentous fungi, examples of which are Aspergillus, Disporotrichum, Penicillium, Neurospora, Fusarium and Trichoderma. The xylanases are stated to be useful in the preparation of bread or animal feed, in breewing and in reducing viscosity or improving filterability of cereal starch.
Shei et al., 1985, and Fournier et al., 1985 describe purification and characterization of endoxylanases isolated from A. niger.
WO 91/19782 and EP 463 706 discloses xylanase derived from Aspergillus niger origin and the recombinant production thereof. The xylanase is stated to be useful for baking, brewing, in the paper making industry, and in the treatment of agricultural waste, etc.